A communication network may comprise a cellular radio network consisting of cells. The cellular telecommunication networks typically operate in accordance with a given standard (or several standards) which sets out what the elements of the network are permitted to do and how that should be achieved. In most cases a cell can be defined as a certain area covered by one or several base transceiver stations (BTS) serving mobile stations (MS) within the cell via a radio interface. Each base-station has a radio transceiver capable of transmitting radio signals in downlink to and receiving radio signals in uplink from the area of a cell next to the base-station. By means of these signals the base station can communicate with the mobile station (MS) terminal in that cell, which itself includes a radio transceiver. Each base station may be connected to a base station controller (BSC) or to any other controller functionality provided by the cellular network. Thus a mobile station (MS) or similar user equipment (UE) within a cell of the system is continuously controlled by a node providing controller functionality. Examples of the network controller include said base station controller (BSC), a radio network controller (RNC) and a mobile switching center (MSC), but other control nodes may also be used for the implementation of the network control functionality. The controller can be linked further to the public telephone network and/or to other networks such as packet data networks. By means of this system a user of the MS can establish a telephone call to the public network via a BS in whose cell the MS is located.
The location of the MS could be fixed (for example if it is providing radio communications for a fixed site) or the MS could be moveable (for example if it is a hand portable transceiver or “mobile phone”). When the MS is moveable it may move between cells of the cellular radio system. As it moves from one cell (the “old cell”) to another cell (the “new cell”) there is a need to hand it over from communication with the BS of the old cell to the BS of the new cell without dropping the call due to a break in communications between the mobile station and the network. This process is known as handover. A need can also arise to hand over a MS whose location is fixed, for example if atmospheric conditions affect its communications with the old BS and call quality can be improved by handing it over to another BS or if there is a need to free up capacity of the old BS.
In some cellular systems a mobile station is capable of making traffic communications with more than one base station at one time. This macrodiversity arrangement allows greater reliability of communications and can reduce the required transmission power. It also means that handovers between one base station and another can be performed in a gradual (“soft”) rather than an abrupt (“hard”) way.
The control node conventionally receives information relating to the quality of communications between the MS and the BSs and optionally other information such as data on the load on at least some of the BSs. The control node uses this information to various functions. For example, by using this information the control node may determine which base station(s) an MS should communicate with and issues instructions to the BS and the MS accordingly.
The mobile station and/or the base station may measure and/or define several indicators or parameters concerning the communication path connection, such as quality of the received signal, signal levels (power) between the receiving and transmitting stations, distance between the stations and so on. The stations can be provided with appropriate means for defining a value for any parameter that can be measured for the interaction between the mobile station and any of the base stations or the radio transmission conditions in a cell.
In a cellular radio communication system, such as the GSM based systems, voice quality in a transmission over a communication path between a base station and a mobile station can be assessed based on a network indicator determined for the connection. Corresponding indicators may be defined both in uplink and downlink.
Currently the most commonly used quality parameter or indicator is so called Bit Error Ratio (BER), which is used e.g. in the GSM (Global System for Mobile) based network systems. The BER is a measure defining the level of quality for data transmission expressed as the relationship between erroneous bits and the total number of transmitted bits. The BER can be defined e.g. by sending a known bit pattern and counting the number of incorrectly received bits in the receiver.
A problem with the BER is that it measures the rate of the bit errors before an error correction mechanism. Therefore it does not take any improvements possibly produced by the error correction mechanism into the connection quality. If the functionality and/or efficiency of the error correction mechanism changes during the operation of the system, the BER values may no longer provide reliable information for assessing the quality of the transmission. The reliability of the BER based quality estimations may also become poorer due to new functionalities introduced into the network. The new functionalities could be such as Frequency Hopping or dynamic Channel Coding.
The inventor of the present invention has identified that frame erasure ratio (FER) could form a network indicator that could be used for the transmission quality estimation and that by using FER at least some of the problems of the BER could be avoided. In general, the FER represents the percentage of frames being dropped due to high number of non corrected bit errors in the frame. The FER can be a measurement of the results of 3-bit cyclic redundancy check for speech channels that is made along with a bad frame indicator (BFI). For signalling channels the FER is a measurement of errors in the block code used for the transmission.
A problem with the FER is that the current terminals do not report downlink FER to the network. There is no appropriate solution to manage the current terminals in a system that may base the connection control to an indicator such as the FER. It would thus be desirable to be able to define the FER or a similar network indicator by some other means than by receiving information of the indicator from a terminal that received the transmission.